Masonry Veneer Support Details: Thermal Bridging

June 3, 2013 – 12th Canadian Masonry Conference – Vancouver, BC

Masonry Veneer Support Details: Thermal Bridging

!   Mike Wilson, MEng, P.Eng Graham Finch, MASc, P.Eng James Higgins, Dipl.T RDH Building Engineering Ltd. Vancouver, BC

Presentation Outline

!   Gravity support systems

!   Design criteria and thermal performance requirements

!   Canadian energy codes

!   Nominal vs. Effective R-Values

!   Thermal modeling and effective R-values

!   Conclusions

!   Slab edge support

Gravity Support Systems for Masonry Veneer

!   Edge-connected steel angles


!   Discretely connected steel angles


!   Structural !   Weight of masonry !   Type of connection !   Backup structural capacity

!   Eccentricity of load !   Section properties of

support member

!   Deflection !   Design criteria

!   Esthetics !   Secondary effects

!   Seismic allowance !   Joint frequency !   Backup movement

Design Criteria

!   Durability !   Material selection !   Compatibility of materials !   Environment conditions

!   Thermal performance !   Design requirement

!   Part 9 (small buildings) !  National Building Code of Canada (NBC), 2010

!  New energy provisions within 2012 update to Section 9.36

!  Provinces adopt the NBC with modifications

!  City of Vancouver (VBBL) is adoption of BCBC

!  Compliance is generally prescriptive (R-value tables)

!   Part 3 (large buildings) !  NBC and Provincial codes reference both:

•  National Energy Code for Buildings (NECB), 2011 – previously the MNECB 1997

•  ASHRAE Standard 90.1 (Energy Code for Buildings Except Low-Rise Residential)

!  Compliance path options (prescriptive, trade-off, modeling)

Overview: Canadian Energy Codes

Prescriptive Energy Code Requirements for Walls in Canada

Climate Zone

Wall – Above Grade: Minimum R-‐value (IP)

8 31.0

7 27.0

6 23.0

5 20.4

4 18.0 N

ECB

201

1 A

SH

RAE

90.1

-201

0 –

Re

side

ntia

l Bui

ldin

g Climate Zone

Wall (Mass, Wood, Steel): Min R-‐value

8 19.2, 27.8, 27.0

7A/7B 14.1, 19.6, 23.8

6 12.5, 19.6, 15.6

5 11.1, 19.6, 15.6

*7A/7B combined in ASHRAE 90.1 No climate zone 4 in ASHRAE 90.1 – bumped to zone 5

!   Effective R-values are required to demonstrate compliance with Energy codes most of the time

!   Nominal R-values do not include impacts of thermal bridging

!   For example nominal R-20 batts within steel studs becoming ~R-9 effective, or in wood studs ~R-15 effective

!   Masonry ties and shelf angles are also thermal bridges that reduce effective R-values significantly (even though a small area)

Effective vs. Nominal R-Values

!   Effective R-values of Building Enclosure Assemblies can be determined by: !   Hand methods – simple wood frame walls, not

suitable for accounting for thermal bridges

!   Laboratory (Guarded hot-box testing) – good for confirmation, expensive and not efficient for multiple configurations

!   Two-dimensional finite element thermal modeling – not accurate for modeling discrete or intermittent elements such as thermal bridges

!   Three-dimensional finite element thermal modeling – most accurate and cost effective. Calibrated with laboratory testing to improve accuracy.

!   Heat3 (Blocon) – 3D finite element software used for this analysis

How are “Effective” R-values determined?

!  Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate gravity support systems

!   Steel stud backup, concrete backup, and exposed slab edge

Thermal Performance of Traditional Veneer Assemblies

Traditional Support Systems: Modelling Results

!  Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate types of “stand-off” gravity support systems

!   Knife plate, HSS Section, and overlapping angles

!   Similar steel & mass and all connected at 48” o/c

Thermal Performance of “Stand-off” Supports Systems

“Stand-off” Support Systems: Modelling Results

Knife Plate HSS Structural Section

Overlapping Angles

shelf angle: 4”x4”x1/4” outside of insulation. 4”x4”x3/4” stand-off knife plates welded to embed plates at 48” o.c.

shelf angle 4”x4”x1/4” outside insulation. 4”x4”x1/4” HSS tube welded to embed plates at 48” o.c.

shelf angle 4”x4”x1/4” outside insulation. 2-6”x4”x5/16” angles bolted to slab edge at 48” o.c.

Nominal Insulation R-Value/U-Value

R-16.8 (RSI 2.95) U-0.060 (USI 0.339)

R-16.8 (RSI 2.95) U-0.060 (USI 0.339)

R-16.8 (RSI 2.95) U-0.060 (USI 0.339)

Effective Assembly R-Value/U-Value

R-14.8 (RSI 2.6) U-0.068 (USI 0.384)

R-14.8 (RSI 2.6) U-0.068 (USI 0.385)

R-15.0 (RSI 2.64) U-0.067 (USI 0.379)

Effective Reduction 16.4% 16.5% 15.3%

!  Modeling performed to look at effective R-values for masonry veneer wall assemblies with alternate proprietary gravity support systems

Thermal Performance of “Proprietary” Supports Systems

Proprietary Support Systems: Modelling Results

Standoff Bracket 4-Bolt Cast-In

shelf angle 4”x4”x1/4” outside insulation. Proprietary clip is ¼” thick steel, 4”x4”x1/4” 6” long C-section. Non-welded connection.

Shelf angle 4”x4”x1/4” outside insulation. Pre-manufactured cast-in place thermal break connection with 4 stainless steel bolts attached to 7”x7”x 3/8” plate.

Nominal Insulation R-Value/U-Value

R-16.8 (RSI 2.95) U-0.060 (USI 0.339)

R-16.8 (RSI 2.95) U-0.060 (USI 0.339)

Effective Assembly R-Value/U-Value

R-14.9 (RSI 2.62) U-0.067 (USI 0.381)

R-16.4 (RSI 2.9) U-0.061 (USI 0.345)

Effective Reduction 16.4% 7%

Impact of Support Spacing

!   Thermal bridging at masonry veneer supports is significant and alone can impact the effective wall R-value of an exterior insulated concrete wall by 27%

!   Design details for “stand-off” conditions that are relatively typical in the industry reduce the overall impact of thermal bridging through continuous exterior insulation to 15-17%

!   Special measures are possible, utilising proprietary systems to reduce the impact of thermal bridging below 10%

Conclusions

Questions

!  Michael Wilson –[email protected]